In general, a flexible tube is made by assembling together two parts manufactured separately: a flexible cylindrical skirt of given length (typically 3 to 5 times the diameter) and a head comprising a neck with a distribution orifice and a shoulder linking said neck to the cylindrical skirt. The head in plastic material(s) can be molded separately and then welded on one end of the skirt but it is advantageously molded and welded to the skirt in an autogenous way by using either an injection molding technique (FR 1 069 414) or a compression molding technique of an extruded preform (FR 1 324 471).
In these two techniques, the skirt is fixed around a punch, one of its ends extending slightly beyond the end of the punch, said punch end acting as the mould for producing the internal surface of the head of the tube (interior of the shoulder and the neck). In these two techniques, one uses a die, which comes up against the end of the punch, the cavity of this die defining the external surface of the shoulder and the neck. The main difference between these two processes resides in the fact that these tooling parts are first of all set firmly together before injection of the plastic material in the first case and that the movement of the tooling parts closing together results in the compression of an extruded preform in the second case.
In the two cases, the end of the skirt extending beyond the punch is caught in the cavity defined by the end of the punch and the cavity of the die. Under the effect of injection or under that of compression, the plastic material comes into contact with the end of the skirt and, raised to a temperature higher than their respective Vicat softening points, the plastic materials of the head and the skirt weld together intimately without any further input of heat or material. After a short maintenance under pressure (of the order of a few seconds) and then cooling, the head is molded according to the required dimensions and welded firmly to the skirt.
The above techniques, which appeared about fifty years ago for the first and about forty for the second, have been improved regularly. At present production rates can be achieved of about 200–250 units per minute. But it now seems that the limit has been reached and no further significant increase in the production rates (beyond 250–300 units per minute) can be reached by simple adaptation of the existing devices.
The applicant therefore tried to produce a new manufacturing apparatus for flexible tubes designed to obtain acceptable economic conditions for significantly higher production rates.